Optical bonding may be used to adhere together two optical elements using an optical grade adhesive. In display applications, optical bonding may be used to adhere together optical elements such as display panels, glass plates, touch panels, diffusers, rigid compensators, heaters, and flexible films such as polarizers and retarders. The optical performance of a display can be improved by minimizing the number of internal reflecting surfaces, thus it may be desirable to remove or at least minimize the number of air gaps between optical elements in the display.
Liquid optically clear adhesives (LOCA) are becoming more prevalent in the display industry to fill the air gap between the optical elements. For example, LOCAs can fill the air gap between a coverglass and indium tin oxide (ITO) touch sensors, between ITO touch sensors and a liquid crystal module, or directly between the coverglass and the liquid crystal module.
Current methods of applying LOCAs either involve a dispensable fluid or the patterning of a thicker, potentially thixotropic, material with the use of a stencil or screen. The use of dispensable fluids involves flowable liquid OCAs such that they behave like a Newtonian fluid. To prevent flow beyond the desired printing area, the use of a pre-cured dam material (matching the refractive index of the LOCA) is often required. This involves an additional process step, and may still potentially lead to overflow of the LOCA if a precise amount is not dispensed and/or there is not perfect coplanarity between the two substrates that are being bonded with the LOCA.
The use of a screen for printing a LOCA has been described in Kobayashi et al. (U.S. Patent Application Pub. No. 2009/0215351). The use of a stencil for printing a LOCA has been described in PCT International Pub. No. WO 2012/036980. Both methods require passing the LOCA through a screen or a stencil to achieve the adhesive coating in the desired area on the substrate.